The present invention relates to a liquid crystal device equipped with microlenses and a liquid crystal display apparatus, particularly a full-color liquid crystal display apparatus, including the liquid crystal device.
In today""s multi-media world, there is an increasing demand for apparatuses and devices which communicate with picture data. Among these, a liquid crystal display apparatus has gained public attention because of its small thickness and small power consumption. A major industry comparable to the semiconductor industry has already developed in that regard. The liquid crystal display apparatus has been principally used in notebook-type personal computers having a picture area size of 10-20 inches, but it is believed to be adaptable to larger-area display apparatuses not only for personal computers, but also for workstations and home television sets.
An increase in picture size is accompanied by problems, such as the need for larger-scale and expensive production apparatuses and the requirement for extensive electrical requirements for driving such large-area apparatuses. These problems lead to a severe increase in production cost, which increases to the second to third power of the picture area increase.
Accordingly, in recent years, attention has been given to a projection-type liquid crystal display system, wherein a small-size liquid crystal display panel is prepared, and a picture displayed thereon is optically enlarged to be displayed to a viewer. This is advantageous because the production of a small-size liquid crystal panel can take advantage of advances in production technology which allow the simultaneous achievement of a smaller size, an improved performance and a cost reduction, similarly as a scaling rule regarding a higher density, a higher definition, a performance improvement and a cost reduction in production of semiconductor devices.
For the above purpose and especially in the case of a TFT-driven liquid crystal display panel, sufficiently small TFTs (thin film transistors) having a sufficient drive power are required; the current trend is a shift from amorphous Si TFTs to polycrystalline Si TFTs and further to TFTs formed on a single-crystalline Si substrate. Accordingly, there has been proposed a liquid crystal display apparatus including an integral structure of a display region and a peripheral drive circuit, wherein not only TFTs but also a peripheral drive circuit such as a shift register or a decoder are integrally formed of polycrystalline Si or single-crystalline Si.
As an example of a liquid crystal display apparatus having such a structure, a projection-type liquid crystal display apparatus is known. In a typical system including the display apparatus, polarized-light is incident to the liquid crystal device to provide emitted light which has been modulated according to given display picture data, thereby enlarging and projecting the emitted light image for viewing. In such a liquid crystal display apparatus, it is a general practice to include a microlens array so as to provide an increased aperture ratio of the liquid crystal device (i.e., areal percentage of aperture given by pixel electrodes), as disclosed in Japanese Laid-Open Patent Application JP-A 8-114780, which discloses a microlens-equipped liquid crystal panel and a liquid crystal display apparatus including the panel. The microlens-equipped liquid crystal panel for this purpose is generally of a transmission type. An example structure thereof is shown in FIG. 10, wherein a liquid crystal layer 17 is disposed between a layer of pixel electrodes 18 and an array of microlenses 16, and respective illumination lights of primary colors R, G and B are incident to the liquid crystal panel at respectively different angles so that the respective primary color lights are caused to enter respectively different pixels or pixel electrodes 18, whereby a color filter layer is removed and an improved light utilization efficiency is realized. This type of projection display apparatus can achieve a bright full-color picture projection display using a single liquid crystal panel, and a commercial product thereof is gradually being introduced on the market.
FIG. 3 shows a basic optical system for a display apparatus including such a known microlens-equipped liquid crystal panel. Referring to FIG. 3, the display apparatus system includes a light source 201, a dichroic mirror 202 of red (R), a dichroic mirror 203 of green (G) and a dichroic mirror 204 of blue (B) for selectively reflecting red, green and blue light fluxes, respectively, from the light source 201, a liquid crystal panel or device 205 for modulating the light fluxes from the dichroic mirrors, a Fresnel lens 206, a projection lens 207, and a screen 208. Parallel light emitted from the light source 201 is separated by the respective dichroic mirrors 202, 203 and 204 into respective light fluxes of R, G and B, which are then incident to the liquid crystal device 205. In the liquid crystal device 205, voltages applied to the liquid crystal at the respective pixels of R, G and B are controlled to effect luminance modulation, depending on given picture data, and the emitted picture data-carrying light fluxes are passed through the Fresnel lens 206 for condensing the light fluxes and the projection lens 207 to be projected in an enlarged size onto the screen 208.
FIG. 2A shows an example of a color pixel arrangement pattern of such a liquid crystal device 205 equipped with microlenses, including microlenses 211, and pixel electrodes 212 including color pixel electrodes 212r, 212g and 212b corresponding to R, G and B, and each having an aperture 213 as shown in an enlarged size in FIG. 2B. G-light separated and reflected by the dichroic mirrors is incident from an upper position of the microlens 211 vertically to the microlens 211 to be converged at a surface of a G-pixel (electrode) 212. On the other hand, R-light and B-light are respectively incident to the microlens 211 with some angles and converged at the surfaces of R-pixel (electrode) and B-pixel (electrode), respectively, thereby providing somewhat distorted circular spots. Each color pixel may have a TFT-structure, e.g., as shown in FIG. 4.
Each pixel shown in FIG. 4 includes a TFT-structure, formed on glass 101, including a gate 106, a source region 150 connected to a data signal electrode, a drain region 103 accompanied by a lightly doped drain region 107, a drain electrode 108 including laminated layers 108a and 108b, and a pixel electrode 508 connected to the drain electrode 108. Opposite the TFT-substrate 101, a counter substrate 621 (on which microlenses are arranged but are omitted from being shown) is disposed, including a black matrix mask 622, for masking regions between adjacent pixels, and a transparent counter electrode 623. The two substrates 101 and 621 are surfaced with alignment films 4010 and 221 so as to align a liquid crystal 611 disposed therebetween.
Such a known microlens-equipped liquid crystal panel is, however, found to be accompanied by problems as follows when the pixel size, i.e., the size of the apertures, is decreased so as to reduce the panel size. When the size of an aperture 213 is reduced relative to a spot diameter formed by condensation with a microlens 211, the distortion of the spot diameter subtly affects the display characteristic. Particularly, when the sizes of the spot diameter and the aperture are nearly equal, part of the spot diameter can be larger than the aperture 213 size due to a spot diameter distortion caused by oblique light incidence, thus resulting in a lower light utilization efficiency. This affects the brightness and color balance. For obviating such difficulties accompanying lowered light utilization efficiency, pixel sizes are ordinarily based on a pixel requiring a larger aperture, whereby the entire device size is enlarged. If the liquid crystal panel size is enlarged, the optical system size is also enlarged, resulting in an increase in the size of the projection-type liquid crystal display apparatus.
Further, if the pixel size is made smaller, another problem is encountered wherein a region 214 of liquid crystal alignment disorder called xe2x80x9cdisclinationxe2x80x9d is caused along one or more sides of a pixel due to a lateral electric field between neighboring pixels, thereby lowering the picture quality. For example, as shown in FIG. 2B (based on a result of analytical study of our research and development group) the alignment films 4010 and 221 (FIG. 4) are rubbed in directions of a solid-line arrow and a dashed-line arrow, respectively, to align homeotropically aligned nematic liquid crystal molecules with a pretilt of 45 degrees in the dashed arrow direction with respect to a normal to the substrates. If the disclination 214 is present in overlapping with a condensed light spot 215, a lowering in contrast leading to a lowering in picture quality, is caused. In order to obviate the hindrance by the disclination 214, it is necessary to reduce the size of the condensed light spot 215 or enlarge each pixel size to lower an effective aperture ratio (i.e., an areal ratio of the aperture 213 to the pixel electrode 212). The latter is contrary to the requirement of a higher resolution. On the other hand, the reduction in size of a condensed light spot requires a complicated optical system. More specifically, light fluxes incident to a microlens are not uniform and uniformization of the light fluxes in one direction before incidence requires a very complicated optical system.
JP-A 7-159771 has proposed a transmission-type color liquid crystal display device wherein color filter segment areas are varied so as to provide a maximum transmittance and an increased color purity of white and respective colors, whereas the use of a color filter is accompanied with a serious drawback of a lowering in brightness.
In view of the above-mentioned state of the background art, a principal object of the present invention is to provide a liquid crystal device (panel) capable of obviating deterioration of brightness and chromaticity even at a reduced panel size and a liquid crystal display apparatus including such a liquid crystal device.
Another object of the present invention is to provide a liquid crystal device capable of providing a full-color projection image free from mosaic appearance and preventing color mixing at a pixel and a liquid crystal display apparatus including such a liquid crystal device.
A further object of the present invention is to provide a liquid crystal device capable of obviating adverse effects, such as deterioration in brightness and chromaticity, attributable to alignment disorder regions, such as disclination, and a liquid crystal display apparatus including such a liquid crystal device.
According to the present invention, there is provided a liquid crystal device comprising: a layer of liquid crystal, two-dimensionally arranged pixel electrodes disposed so as to apply voltages to the liquid crystal and, together with the liquid crystal, form two-dimensionally arranged pixels each corresponding to one pixel electrode and designed to emit light of one of a plurality of colors, and an array of microlenses disposed to illuminate each pixel with a condensed light spot of illumination light of one of said plurality of colors, wherein pixels of at least one of said plurality of colors are set to have a pixel size different from those of pixels of the other color(s). Herein, the xe2x80x9cpixel sizexe2x80x9d means an effective pixel size which is generally determined by a size of an aperture of a pixel electrode. As a result, it is possible to provide a liquid crystal device capable of exhibiting good color balance and light utilization efficiency while obviating an increase in the entire size of the liquid crystal device.
According to another aspect of the present invention, in the type of liquid crystal device described above, the plural colors are three primary colors; the pixels for the three primary colors are arranged two-dimensionally in a first direction and a second direction, so that pixels for two of the three primary colors are arranged alternately at a first pitch in the first direction, and pixels for a different two of the three primary colors are arranged alternately at a second pitch in the second direction; the microlenses are arranged two-dimensionally at a pitch twice the first pitch in the first direction and at a pitch twice the second pitch in the second direction.
In other words, pixels of a first primary color and a second primary color are arranged alternately at a first pitch in the first direction; pixels of the first primary color and a third primary color are arranged at a second pitch in the second direction; the microlenses are arranged two-dimensionally at a pitch twice the first pitch in the first direction and at a pitch twice the second pitch in the second direction.
When combined with an illumination optical system designed for illuminating the liquid crystal device with the primary color lights from different directions, reflected light fluxes of the primary colors after modulation at three pixels of R, G and B forming a pixel unit are allowed to be emitted through one microlens, thus providing an RGB mosaic-free high quality color picture projection display.
More specifically, the first color illumination light flux is caused to form a condensed light spot (focal spot) at the first color pixel by incidence through a microlens right above the first color pixel and, after reflection, emitted through the same microlens. The second color illumination light flux is caused to form a focal spot at the second color pixel by incidence through a microlens shifted in the first direction from a position right above the second color pixel and, after reflection, emitted through the microlens right above the first color pixel and adjacent to the microlens of incidence. The third color illumination light flux is caused to form a focal spot at the third color pixel by incidence through a microlens shifted in the second direction from a position right above the third color pixel and, after reflection, emitted through the microlens right above the first color pixel and adjacent to the microlens of incidence. As a result, each microlens is caused to emit reflected light fluxes from the first color pixel light therebelow and the second and third color pixels adjacent to the first color pixel in the first and second directions, respectively. More specifically, the first color pixel is disposed right below the center of each microlens, and the second and third color pixels are disposed below boundaries of the microlens with adjacent microlenses in the first and third directions, respectively. In this case, light fluxes from the respective color pixels are made substantially parallel while being passed twice through a microlens, so that it is possible to form a bright projected image on a screen even when using an inexpensive projection lens having a small numerical aperture.
In a preferred embodiment, each microlens is disposed to have an optical axis for forming the condensed light spot, which optical axis is shifted from the center of an associated pixel. As a result, it is possible to form a condensed light spot at an associated pixel while obviating a disclination region in the pixel, whereby the above-mentioned effects are enhanced to provide an effective liquid crystal device free from deterioration of brightness and chromaticity.
According to another aspect of the present invention, there is provided a liquid crystal display apparatus including the above-mentioned liquid crystal device, an illumination means for illuminating the liquid crystal device with illumination light of the plurality of colors so that modulated illumination light of the plurality of colors is emitted from the liquid crystal device, and a projection means for receiving the modulated illumination light emitted from the liquid crystal device to project picture light.
According to still another aspect of the present invention, there is provided a liquid crystal display apparatus including: a plurality of liquid crystal devices each comprising a layer of liquid crystal, and two-dimensionally arranged pixel electrodes disposed so as to apply voltages to the liquid crystal and, together with the liquid crystal, form two-dimensionally arranged pixels each corresponding to one pixel electrode and designed to emit light of one or plural colors; an illumination means for illuminating the plurality of liquid crystal devices with illumination light of corresponding color(s) so that modulated illumination light of the corresponding color(s) is emitted from each liquid crystal device; an optical synthesis means for synthesizing the modulated illumination light emitted from the plurality of liquid crystal devices; and a projection means for receiving the synthesized modulated illumination light to project picture light; wherein pixels of at least one among a total of said one or plural colors of the plurality of liquid crystal devices are set to have a pixel size different from those of pixels of the other color(s).
Further, if the pixel electrodes are constituted as reflective electrodes, it is possible to provide a reflection-type liquid crystal device having a high aperture ratio and providing a bright high quality picture.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.